Process of degreasing



Apri l1, 1939. Y A A. LEvlNE 2,153,577

' PROCESS oF DEGREASING Filed March '7, 1935 wafer raror Wafer Separador MMI -U l WH HHUII INVENTOR. 41 APehurA. Levine ATRNEY Wai-er l' rafentednpr. 11,. 1939 PATENT OFFICE j PROCESS 0F DEGREASING Arthur A. Levine, Niagara Falls," N. Y., assigner to E. I. duA Pont de Nemours &` Company, Wilmington, Del., a corporation of Delaware ."-Aptucatitn Maron 7.11935, sei-iai No. 9,911

's claims.

'I'his invention relates -to a novel degreasing process and-apparatus. More particularly it is concerned with a method of degreasing metal articles with various solvents to remove grease and other impurities therefrom. Among' the various solvents suitable for use in degreasing may be mentioned in particular the chlorinated hydrocarbon solvents such as trichlorethylene, perchlorethylene, ethylene dichloride, dichlorethylene, carbon tetrachloride, and various mixtures of these solvents. This invention also includes, .as a novel composition, a liquidfor use in degreasing and comprising one of these halogenated hydrocarbon solvents containing dissolved therein a small amount of an added agent.

In the degreasing of metal articles the removal of cutting oil residues which may remain on the articles has presented aserious and as yet unsolved problem. When machineqpartshand- 20 other objects are stamped, machined, or otherwise worked upon, a cutting oil is very irequent- 1y employed to assist in the mechanical operation. This oil ordinarily consists of a soapwater emulsion. Afterthe machine operation isv completed a soapy residue which may contain in addition to soap, a greater or less amount of water, oil and various other ingredients, is.

' left o n the metal. When the metal article is subsequently degreased. as for example by immersion in a bath consisting of a chlorinated hydrocarbon solvent in either liquid or vapor form, the soapy residue is not readily removed from the article because the soap is not soluble to any sub- .stantial degree in the chlorinated hydrocarbon solvent. 'Ihis has been a serious disadvantage in the use of the halogenated hydrocarbons in degreasing operations on metal parts containing oil residues, and, in general, themethods'now known do not yield entirely satisfactory results.

One of the objects of this invention -is to devise a process which will successfully remove cutting oil residues from metallic parts being degrea'sed during the degreasing operation. An-

other object of this invention is to Vprovide means by which the soapy residueis broughtinto solution in the chlorinated hydrocarbon solvent which is used for degreasing. Another object of this invention is' to provide means'by which the chlorinated hydrocarbon solvent employed 50 is continually purified and returned to take part' in further degreasing operations. Still another object of the invention is .to remove water from the solventso that substantially water-free chlorinated hydrocarbon solvent is returned for sub- 55 sequent use. These and still further objects of my invention will be apparent from the ensuing disclosure. s f

In the description of the process which follows the degreasing solvent will be referred to as trichlorethylene. This is the preferred sol- 5 vent for use in my process, although, as indi-f cated above, other liquids may also be suitable. Among other solvents may be mentioned halogenated hydrocarbons,l particularly the chlorinated hydrocarbons, hydrocarbons, and petroleum fractions such 'as benzine, naphtha, etc. However, it may be mentioned at this. time that in order for the water removal phase of my process to be carried out effectively it is necessary Y that a solvent be selected which has a specific gravity greater than that of water. For this reason the halogenated hydrocarbons are the solvents with which the invention is most directly concerned'. y Y

My novel process will be described with reference to the annexed drawing which is illustrative of a form of apparatus for carrying out my invention. By so describing the method I do not, of course, mean that it is restricted to use with this apparatus. The apparatus shown is merely a convenient and preferred way of utilizing my method in the removal of cutting oilresidues from metallic parts being degreased.

- In the drawing, Fig. l represents a 'schematic view of the entire equipment including various $0 baths of liquid solvent in which the metal parts 2 is a detail view, also schematic, of a water sep- 35 arator which may be employed in conjunction with the apparatus of Fig. 1. l

In the drawing the numeral 5 represents a' v container in which the degreasing liquids and the other necessary elements are positioned. shown, this container is divided into three compartments by means oi thetwo interior bailies 6 and 1. These compartments are numbered respectively 8, S and I0 and containvarious liquids to be presently described.

As shown, the baille 1 has positioned near its upper end an overflow opening i2 which permits communication between chambers 9 and Il). Similarly, in the container wall 5 there is positioned an aperture I3 through lwhich the 50 liquid in compartment 8 may ilow out. After emerging from compartment 8 this liquid flows through a pipe-line tobe presently described.

Positioned at the bottom of each compartment is a series of steam pipes which are all indicated 55 Y through which steam or some other `three baths are brought in the drawing by the numeral Il. These pipes,

heating medium may be conducted, serve to volatilize the solvents in the various compartments and maintain the liquids at the boiling points. 'I'he vapors of the solvent, which in the installation being described is trichlorethylene, lill the space within the container below the condensing coils I 9 to .be presently described. This vapor space is Vindicated by the numeral I6.

At the upper portion of the apparatus and completely encircling the interior periphery thereof is positioned a trough I1. This trough is lower at the outlet where it is connected with pipe-line I8 than at any other portion of its extent. Above the trough and also extending along the entire interior periphery of the apparatus are the condensing coils I9 through which a cooling medium flows. This cooling medium, which may be water or `some other liquid, serves to condense the vapor presentv in vapor space I6 and the condensate collects in the trough I1. Due to the iact that a portion of the trough I1 adjacent to pipe-line I8 constitutes what is in effect a sump, the condensate flows in the trough around to this point where it is removed from the apparatus by pipe-line I 8.

In the compartment 8 trichlorethylene Icon'- taining dissolved therein a small amount of oleic acid is initially placed. Details of this solvent composition and the possibility ot substituting other materials for the oleic acid in the solvent mixture will be described subsequently. In compartment 9 pure trichlorethylene containing no dissolved oleic acid is placed. In compartment III a small amount of pure trichlorethylene may also be placed. Because of the steam pipes the to the boiling point and the vapor space I8 Vigorous boiling is necessary in order to effect the solvent purication phase of my invention, presently to be described. 1

As previously mentioned, a portion of the solvent in compartment 8 willoveriiow through the outlet I8 whence it is then conducted away through the pipe-line 20 to water separator 2|. The liquid in compartment 8 should consist of pure trichlorethylene containing dissolved therein oleic acid for eilicient operation, but in use water may be introduced thereinto either-by the articles being degreased or in various other ways. This water being lighter than ene will tend to rise to the top and consequently the 'liquid owing out through outlet Il to pipeline 29 may include water as one constituent. any water from The water separator 2| removes the mixture and the puried trichlorethylene flows outwardly through pipe-line 22 into. compartment I through inlet 28. The water removed by the separator flows out through exit line 24. It is thus evident that trichlorethylene free from water is transferred from compartment 8 to compartment I9 where it is vciatilized lilling the vapor space I8 and then, upon condensation, falls into the trough I1.

'I'he overflow outlet I2 providing communication between chambers 9 and IIlhas previously been referred to. This permits the pure trichlorethylene to ilow from compartment 9 to compartment I Il. Thus, compartment I9 receives the trichlorethylene i'ree from water from both of the other compartments.

As is well known from considerations of physical chemistry any high boiling material dissolved in the trichlorethylene or other solvent will not is Illled with vapor.

the trichlorethyl- Vbe carried over into the vapor phase when the liquid is volatilized but will remain behind unvolatilized, as a liquid. Accordingly the vapor space I8, supplied by the ebullition of solvent in chambers 8, 9 and I0, will not contain any oleic acid but will consist of substantially pure trichlorethylene vapor together with any water vapor which may be volatilized. It is obvious, of course, that after use some water may find its way into the apparatus and might be volatilized. 'I'hus the vaporization of trichlorethylene and its condensation by means of cooling coils I9 serves to purify the solvent, any high boiling impurity such as the oleic acid being left behind. Soap removed in the degreasing process is not carried over into the vapor phasebut is also left behind. 'I'he condensate collecting in trough I1, pure trichlorethylene and water, ows out through the pipe-line I8 into water separator 25 which may be of the type illustrated in Fig. 2. Here the water is removed and ilows out through .pipe-line 28 whereupon substantially pure trichlorethylene is returned by pipe-line 21 to the apparatus. As indicated, means are provided comprising conduits 28 and 29 to supply this purified liquid trichlorethylene respectively to compartments 8 and 9, Valve means 3| and 32 are positioned in these conduits s'o that these chambers may be supplied with relative amounts of the solvent at will. In practice I have found it desirable to supply -just enough solvent to the chamber 8 to maintain a suillcient head of liquid to cause the liquid to llow out through outlet pipe I3, whereas the quantity supplied to compartment 9 should be suillcient to keep this bath in a substantially pure state.

Vaporization, condensation, water removal, and return of the puried solvent to the chambers 8 and k8 are carried out at a rate rapid enough to maintain in these two chambers solvent i'ree from dissolved soap and water. The liquid in compartment 8 contains dissolved oleic acid o1' course while that in compartment 9 should be substantially pure trichlorethylene freed from dissolved materials. By keeping the liquids in 'all three compartments at the boiling point and by condensing the vapor and returning purified condensate, it is. possibleto purify the solvent continuously during the process.

The operation of my improved process as applied to the degreasing of metal parts containing cutting oil residues may be as follows. As

previously stated, these cutting oils all contain soap and some water; and/or an oily ingredient in greater or less amount may also be present. I have found that although soap will not dissolve readily in chlorinated hydrocarbon solvents such as trichlorethylene alone, all soaps are relatively soluble in such a solvent if oleic acid in amount from 1 to 5% is present therein.

Accordingly the iirst step inmy process is to immersethe article containing the cutting oil residue in the liquid of compartment 8 which consists of trichlorethylene with oleic acid dissolved therein. Due to the presence of the oleic acid the soap will dissolve in the trichlorethylene and when the metal is removed it should be substantiall'y free from grease and oil, as well as from the soapy residue. It may, however, contain on its surface small traces of oleic acid.

Accordingly the next step in my process is to immerse the metal in the solvent of compartment 9. This removes any small traces or' oil or l the step of immersing it in the liquid solvent of compartment 9. However, forthis to be effective it is necessary that the metal be ilrstcooled so that its temperature is below the boiling point of the vapors. It is only in very exceptional circumstances that the employment of such a step l will be of value but I `wish to mention this so that the process as described will be construed to include this step if the vapor rinse treatment is found to be necessary. y,

After completing the degreasing operations described, it is obvious that the solvent in compartment 8. will contain dissolved oleic acid and soap. When it is removed through overflow outlet Il and allowed to flow into compartment Il, the dissolved soap will be carried over into this compartment with the solvent overiiowing. Owing to the fact that this is primarily a distillation compartment the soap will tend to accumulate therein since it is not carried over into the vapor space II when the solvent is v olatilized.

Similarly the solvent in compartment 9- is puriiled by overowing continually into compartment Il where it is volatiliaed. After condensation and removal of the water the pure solvent is returned to chamber 9 (as well' as to chamber I) by the conduits previously described, and this serves to keep the liquid in compartment 9 in a pure state. The relative amounts of purified solvent returnedto compartments 8 and 9 are, as

The halogenated hydrocarbon is illustrated on the previously indicated, sufficient to provide a substantial overow head through the overflow outlets permitting egress of a portion of the volume of solvent from each chamber. v

The apparatus in Fig. 2 illustrates only on type of the various water separators which might be used in practicing my invention. As shown, the solvent-water mixture iiows in through entrance pipe 35 and the trichlorethylene tends to drop to the bottom by reason of its higher gravity.

drawing by the number ll.. The water tends to form a supernatant .layer-I1. The baille 38 is 'positioned in the housing. so as to aid sep- A aration of the liquids into two layers. The supernatant layer of water then i'iows outl through outlet ll whereas the trichlorethylene overilows into outlet pipe Il and th's ilows out from the separator. The numeral 42 indicates a vent opening which permits any vapor present to escape to the external atmosphere.

The novel composition suitable ford metal parts containing soapy residues and consisting of a solvent in which is dissolved a fatty acid such as oleic acid in amounts-ranging from 1 to 5% also forms a part of the invention. Larger amounts of the acid may be 'employed with equal success although I have found the amounts indicated to yield most satisfactory reanni. Amounts lem than 1%- nilv! emdent total results if the quantity oi' soap present on the` articles being degreased is not too great. Oleic acid is my preferred addition agent, principally by reason of its relatively low cost, but other higher fatty acids, such as stearic, palmitic, linoleic, recinoleic, may also be utilized.

Various changes may be made in the invention as disclosed without departing fromthe essential principles thereof. It 'is to be understood that the disclosure in so far 'as it relates to speciiic amounts and' procedure is to be considered as merely illustrative and the scope of my invention is to be construed solely in accordance with the appended claims.

I claim:

l. A method of degreasing metallic parts containing cutting oil residues which` comprises" immersing said metallic parts in a solvent which consists of liquid trichlorethylene containing oleic acid dissolved therein, withdrawing said articles from said bath and then immrsing them in a bath of clean trichlorethylenein order to remove traces of oleic acid and grease remaining on said articles.

' 2. In an apparatus for degreasing metal articles, three contiguous compartments, the rst. compartment being adapted to contain a bath of trichlorethylene containing oleic acid dissolved therein, the second compartment being adapted to contain substantially pure trichlorethylene, and the third compartment being adapted to contain trichlorethylene in which is dissolved the greater part of those impurities removed from the metal articles which have been degreased in said first two compartments, means for withdrawing trichlorethylene and water iioating thereupon from said first compartment, means for separating the trichlorethylene from the water, and means forreturning the separated trichlorethylene to said third compartment.

3. In anapparatus for degreasing metal articles, three contiguous compartments, the irst .the liquid in said first and second compartments to said third compartment in order that said vimpurities removed from said metal articles may collect in said third compartment, means. including a heater and a condenser, for purifying and replenishlng the solvent thus removed from the baths contained in said first and second com.- ,partmenta means for withdrawing trichlorethylene from the water oating thereupon from said first compartment, means for separang `the trichlorethylene from the water and means for i returning the separated trichlorethylene to said` third compartment.

' sama 1i. uvm 

